Proposed studies are aimed at determining the physiological processes in the small intestine that are associated with and responsible for immunity to Trichinella spiralis. The hypothesis to be tested is that the overall immune response is a biphasic phenomenon: an early response, which occurs within the first 24hrs after challenge. It is hypothesized that the initial or "fast" response: (a) prevents the actual establishment of infective larvae, (b) does not involve inflammatory cell influx into the lamina propria, and (c) causes subtle pathophysiologic changes. In contrast, the delayed or "slow" response is: (a) directed at dislodging and expelling previously established worms, (b) characterized principally by acute mucosal inflammation, and (c) attended by many of the pathophysiologic changes associated with worm expulsion in a primary infection. Emphasis will be placed on characterizing and establishing the relative importance of the "fast" response. To test the proposed hypotheses experimentally, correlations will be made during challenge infections between worm burdens and an array of structural and physiological parmeters in the small intestine. These correllations will be made with regard to the spatial distribution of the parasite in the gut, and will be made beginning as early as 15 min following challenge. These studies will be carried out on a temporal basis until worms are completely expelled from the intestine and physiological parameters return to normal. Specific roles of factors such as intestinal motility, intestinal secretion, prostaglandins and intestinal mucous production in acquired resistance will be examined.